Bibliographic details of the publications referred to by author in this specification are collected alphabetically at the end of the description.
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
Acute myocardial infarction (AMI) following coronary artery occlusion is the single largest cause of death in developed countries. Approximately 10% of patients die suddenly in the first few days due to arrhythmias or cardiac rupture, while 50% will develop heart failure within 2 years.
Occlusion of a coronary artery results in hypoxia and leads to cardiomyocyte necrosis, which initiates a complex response that can be considered in 3 phases: an initiation phase, an acute inflammatory phase and a repair phase (Frangogiannis, Pharmacol Res. 2008, 58:88-111). Ultimately, this process leads to fibrosis with left ventricular (LV) remodelling, a compensatory mechanism to maintain cardiac output. The deleterious effect of AMI on LV function is dependent not only on the size of the infarct but also on the balance of inflammation and repair.
Within minutes of ischaemia, the innate immune system is initiated by complement activation, expression of the Toll-like receptor 4 (TLR4) and generation of reactive oxygen species (ROS). In animal models, inhibition of complement reduces the inflammatory reaction and improves LV function, however these benefits have not been reproduced in human trials (Armstrong et al. 2007, Jana 297:43-51; Granger et al. Circulation. 2003, 108:1184-1190; Mahaffey et al. Circulation. 2003, 108:1176-1183). Prevention of the initiating phase by inhibition of TLR4 is also effective in animal models but not yet tested in humans (Timmers et al. 2009, J Am Coll Cardiol. 53:501-510). Targeting ROS is unlikely to be useful because ROS is generated within minutes of ischaemia (Lefer and Granger, Am J Med. 2000, 109:315-323).
The acute inflammatory phase begins within hours of ischaemia and is characterised by a cellular infiltrate of neutrophils and M1-like macrophages, together with a large number of ‘pro-inflammatory’ chemokines and cytokines. Neutrophils, which accumulate rapidly within the first 24 hours, are a rich source of matrix metalloproteinases (MMP) that assist clearance of dead cells and debris. M1-like macrophages are the other major cell type present during the acute inflammatory phase. Migration to the site of ischaemia is mediated by binding of CCR2 to high levels of MCP-1 (CCL2). Granulocyte-macrophage colony stimulating factor (GM-CSF) promotes production of inflammatory cytokines (TNF-α, IL-6 and IL-1β) by M1-like cells (Fleetwood et al. 2007, J Immunol. 178:5245-5252).
Several strategies to inhibit the inflammatory phase have been tested with varying success. Targeting specific inflammatory cytokines has produced mixed results. TNF-α-deficient mice had improved LV function after AMI, however, administration of an inhibitory soluble TNF receptor impaired LV function (Monden et al. 2007, Cardiovasc Res. 73:794-805; Sun et al. 2004, Circulation. 110:3221-3228). Similarly, inhibition of IL-1 has shown either beneficial or deleterious effects (Hwang et al. 2001, J Am Coll Cardiol. 38:1546-1553; Suzuki et al. 2001, Circulation. 104:I308-I303). These results suggest that targeting individual cytokines may not be useful.
The current treatments for patients with myocardial infarction are revascularization with thrombolytic agents or interventional procedures. These treatments have focused on restoring blood flow to the ischemic tissue to prevent tissue necrosis and preserve organ function. The most recent recommendations from the American Heart Association for patients presenting with myocardial infarction include fibrinolysis within the subsequent 30 minutes and primary percutaneous coronary intervention (PCI) by 90 minutes after patient presentation (Masoudi et al., 2008; Anderson et al., 2011). The introduction of therapies including aspirin, anti-platelet drugs, ACE inhibitors, ARBs, β-adrenoceptors antagonists, Ca2+-channel antagonists, anti-thrombolytics, and glycoprotein (GP) IIb/IIIa inhibitors has improved outcomes post myocardial infarction. Although the majority of these pharmacotherapies remain in clinical use, myocardial infarction and resultant heart failure remains a major cause of death and disability.
The restoration of blood flow after a period of ischaemia, however, may elicit further myocardial damage, known as reperfusion injury. The manifestations of reperfusion injury include arrhythmias, myocardial stunning, microvascular dysfunction and incomplete recovery of contractile function, in addition to significant cardiomyocyte loss. It has been suggested that an overproduction of reactive oxygen species (ROS), intracellular Ca2+ overload and inflammatory cell infiltration are the most important features of myocardial ischaemia-reperfusion (I-R) injury.
During reperfusion of ischemic myocardium, myocardial necrosis triggers a sterile inflammatory response through the release of endogenous molecules that have been designated as Damage-Associated Molecular Patterns (DAMPS) (Chen, G. Y. and G. Nunez, Sterile inflammation: sensing and reacting to damage. Nat Rev Immunol, 2010. 10(12): p. 826-37). These molecules are sensed by receptors that are also involved in microbial pathogen recognition and inflammatory response. One such group of receptors that have been implicated in myocardial ischaemia reperfusion injury are the Toll-like receptors (TLRs) (Arumugam, T. V., et al., Toll-like receptors in ischemia-reperfusion injury. Shock, 2009. 32(1): p. 4-16; Chao, W., Toll-like receptor signaling: a critical modulator of cell survival and ischemic injury in the heart. Am J Physiol Heart Circ Physiol, 2009. 296(1): p. H1-12). TLR4, the receptor for Gram negative bacterial cell wall component lipopolysaccharide (LPS), is expressed on cardiomyocytes and is responsible for LPS-induced myocardial dysfunction in endotoxaemia (Cha, J., et al., Cytokines link Toll-like receptor 4 signaling to cardiac dysfunction after global myocardial ischemia. Ann Thorac Surg, 2008. 85(5): p. 1678-85; Tavener, S. A. and P. Kubes, Cellular and molecular mechanisms underlying LPS-associated myocyte impairment. Am J Physiol Heart Circ Physiol, 2006. 290(2): p. H800-6).
Despite the understanding of the physiology of cardiac ischaemia-reperfusion injury, and even though there are interventions based on the basic pathogenesis of myocardial ischaemic-reperfusion injury, such as antioxidants and Ca2+ channel blockers, clinical studies have shown limited success. Accordingly, methods of treating this condition both effectively and reproducibly, so as to reduce cardiac injury, have remained elusive. There is therefore an ongoing need to develop methods of treating patients who experience a myocardial ischaemia episode so as to minimise the myocardial tissue damage which is triggered by prolonged ischaemia, and which damage can be rendered still more severe when reperfusion occurs. The objective is to maintain and/or restore myocardial functionality both in terms of cardiomyocyte viability and contractile function.
To this end, the therapeutic potential of the glucocorticoid (GC)-regulated anti-inflammatory mediator annexin-A1 (ANX-A1) has recently been recognised in a range of systemic inflammatory disorders. ANX-A1 binds to and activates the family of formyl peptide receptors (FPRs), which are members of the seven transmembrane G protein-coupled receptor (GPCR) family, to inhibit neutrophil activation, migration and infiltration.
The FPR2 member of the human FPR family (also comprising FPR1, and FPR3) is now identified as the receptor responsible for some of the biological activities of ANX-A1, its N-terminal peptide and LxA4 (Ye et al., 2009) and a large number of other ligands. The FPR1 and FPR2 receptors are widely distributed in tissues and different cell types, being most prominently expressed on cell types involved with inflammatory processes, whereas FPR3 is thought to be highly expressed only in dendritic cells. FPR2 and FPR3 however share ≥70% level of sequence homolog (Ye et al, 2009). Studies on the cardioprotective actions of ANX-A1 and its peptide mimetics (Ac2-26, CGEN-855A) have largely focused on its anti-inflammatory effects as a mechanism of preserving myocardial viability following I-R injury. However, there is also now evidence of the direct protective action of ANX-A1 on myocardium, independently of inflammatory cells in vitro. The ability of ANX-A1 to preserve both cardiomyocyte viability and contractile function, in addition to reducing neutrophil infiltration (anti-inflammation) has therefore highlighted the potential therapeutic utility of ANX-A1 as a clinical approach to improving outcomes after myocardial infarction. Nevertheless, this approach is still undergoing extensive research and its approach is not yet deployed in the clinic. Accordingly, the need for development of new treatment regimes for use with myocardial I-R injury is ongoing.
It has been observed that although the ANX-A1-FPR2 interaction exemplifies one possible means of treating myocardial infarction patients, there are still unwanted side effects associated with this interaction. In particular, FPR-mediated signalling can lead to localised Ca2+ overload in a reperfused tissue and thereby the induction of cell death. In work leading up to the present invention, however, an FPR agonist has been identified which unexpectedly exhibits highly selective functionality in terms of inducing FPR-mediated signalling. Specifically, in addition to selectively inducing FPR1 signalling (as opposed to FPR2 signalling), the compounds of the present invention also effect a functional bias in that only the FPR1-ERK/Akt mediated signalling pathways are upregulated, which, surprisingly, selectively activates cardiomyocyte survival mechanisms without the concomittant activation of intracellular Ca2+ mobilisation that is usually observed with FPR activation. Still further, FPR1 mediated signalling has been determined to effect not just the restoration of cardiomyocyte contractile function, but also the preservation of cardiomyocyte viability thereby providing not just an effective alternative to ANX-A1/FPR2-related cardiomyocyte survival effects, but, in fact, a significantly improved effector mechanism which, unlike FPR2 activation, permits selective upregulation of only ERK/Akt signalling and not intracellular Ca2+ mobilisation. Accordingly, the present invention provides unexpected and superior outcomes relative to what was previously known in relation to treating myocardial infarction, and in particular ischaemia-reperfusion injury, via the selective upregulation of FPR1-ERK/Akt signalling. The present invention has therefore enabled the development of a treatment method in respect of which the undesirable side effect of Ca2+ overload and potentially also Ca2+-triggered pro-inflammatory effects have been minimised, while nevertheless upregulating myocardial contractile function and viability, using a single compound which both selectively upregulates FPR1 activity and also skews the induced receptor signal to a cytoprotective ERK/Akt-mediated response.